Google Photos finally begins to allow tag people manually; or so they say several reports from the United States. Unfortunately we have no direct feedback. The automatic function has been present for a long time (it also came from us recently, but continues to have mixed results), but in the event of a software error it was never possible to intervene. Now yes, but to an important condition.
It is not possible to specify to the software where there is a face, just tell them who the automatically detected ones belong to. If Google is wrong and does not detect anyone, it is still not possible to get around. The hope is that this is the next step, although it is better to avoid establishing a release date, given how things have gone so far.
Google has not released detailed information on how the update is distributed: it appears to be happening server side gradually, as usual, but it is still necessary to have the latest version of Foto. In short, it's up to you to wait for it to "magically" appear on our devices.